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I92                              MOLYBDENUM STEELS

aqueous solution by hydrogen sulphide, the sulphide separated and ignited
to the trioxide, which can be purified if necessary and weighed.

Procedure. 2-3 grams of the sample are treated, in a small, covered
porcelain dish, with nitric acid (D = 1-18), the solution evaporated to dry-
ness, the residue ignited gently to decompose the nitrates, and the oxides
obtained fused with sodium peroxide in a nickel crucible, as indicated for
the analysis of chrome steels. The mass is lixiviated with hot water, sodium
peroxide being added if the mass appears greenish owing to the presence of
manganates, and the liquid boiled and filtered, hot water being used for

washing.

The residue is dried and fused with sodium carbonate, and the fused
mass lixiviated with hot water to recover any small quantities of molybdenum
remaining in the residue insoluble in water. The two liquids—which may
contain, besides the molybdenum as sodium molybdate, also vanadium,
tungsten, chromium, phosphorus, silicon, etc.—are united and, if in presence
of large quantities of molybdenum, made up to a definite volume, of which
an aliquot part is taken for the determination ; where, however, the quantity
of molybdenum is small, the whole of the filtrate is taken.

The volume of the solution is reduced to 50-60 c.c., most of the alkali
neutralised with sulphuric acid, 25 c.c. of concentrated ammonia solution
added and the solution treated with hydrogen sulphide. After some time
the liquid is acidified with dilute sulphuric acid,1 heated to boiling and
allowed to cool, the current of hydrogen sulphide being continued through-
out. The molybdenum sulphide is filtered through a tared Gooch crucible,
washed first with water acidified with sulphuric acid and then with alcohol,
and dried at 100°. The crucible, covered with a clock-glass, is placed in
a fairly roomy nickel crucible and heated with a small flame to convert the
molybdenum sulphide into trioxide. As soon as the odour of sulphur dioxide
ceases, the clock-glass is removed and the heating continued to constant
weight, the base of the nickel crucible being kept incandescent.

The weight of the molybdenum trioxide—which is pale yellow if pure
—multiplied by 0-6667, gives the molybdenum present.

In some cases the molybdenum trioxide may contain small quantities
of silica. In such case the weighed trioxide is dissolved in ammonia in the
crucible, the residual silica being washed, dried and weighed. If vanadium
is present (brown coloration of the trioxide) the weighed oxides are dissolved
in a little sodium hydroxide solution and the vanadium determined, in the
alkaline solution (see Vanadium Steels), the weight of the vanadium pent-
oxide (V20S) being subtracted from that of the molybdenum trioxide found.

2.  Determination of the Silicon and Tungsten.—The procedure
followed is that given for estimating these elements in tungsten steels.

3.  Determination of the Carbon, Manganese, Phosphorus and
Sulphur.—The methods used with ordinary steels are applicable (see Iron,
i. 3, 4, 5)-

4.  Determination of the Chromium.—The chromium is estimated
in an aliquot part of the aqueous solution from the lixiviation of the mass

1 If tungsten is present, acidification is preceded by addition of a little tartaric
acid to prevent the precipitation which would otherwise occur.arts of sulphur require 257-7 Parts of iodine or i gram of sulphur,